This invention relates to halogen-substituted hydrocarbons containing fluorine, and more particularly, to a process for reducing the fluorine content of hydrofluorocarbons and hydrohalofluorocarbons.
Hydrofluorocarbons (i.e., compounds containing only the elements carbon, fluorine, and hydrogen) and hydrohalofluorocarbons (i.e., compounds containing only the elements carbon, fluorine, hydrogen and chlorine and/or bromine) are widely used as refrigerants, aerosol propellants, blowing agents, cleaning agents, fire extinguishants and chemical intermediates. Commercially, many of such compounds are prepared by the reactions of hydrogen fluoride with olefins or saturated compounds containing chlorine. Some compounds (e.g., various hydrofluorocarbons) can be prepared by the hydrogenolysis of an appropriate chlorine and/or bromine-containing precursor. These processes can also produce halogenated hydrocarbons having a lesser commercial value and/or not having the desired properties. Furthermore, the supply/demand situation for any particular product can vary and there may be an oversupply of a particular hydrofluorocarbon or hydrohalofluorocarbon. For environment al reasons, it may not be advantageous to dispose of surplus or by-products by such methods as incineration, but rather to further react these materials to increase the yields of useful products. A reduction of the fluorine content of various hydrofluorocarbons and hydrochlorofluorocarbons can improve their value as commercial products and/or as precursors for producing other useful products.
This invention provides a method for reducing the fluorine content of an acyclic saturated compound of the formula CnFaXbHc wherein each X is independently selected from the group consisting of Cl and Br, and wherein n is 1 to 6, a is 1 to 13, b is 0 to 12, c is 1 to 9, and a+b+c equals 2n+2. The method comprises the step of reacting the acyclic saturated compound with HCl in the vapor phase at an elevated temperature in the presence of a catalyst, the mole ratio of HCl to the acyclic saturated compound being at least about 1:1.
The present invention provides a process for reducing the fluorine content of an acyclic saturated compound of the formula CnFaXbHc wherein each X is independently selected from Cl and Br, and wherein n is 1 to 6, a is 1 to 13, b is 0 to 12, c is 1 to 9, and a+b+c equals 2n+2, by reacting the acyclic saturated compound with HCl in the vapor phase in the presence of a catalyst. Of particular note are embodiments of the invention where n is 1, embodiments of the invention where n is 2, and embodiments of the invention where n is 3. Where n is 2 or more, the reaction products having reduced fluorine content may include saturated and/or olefinic compounds. For example, CH3CF3 may be reacted to produce saturated compounds (e.g., CH3CClF2 and CH3CCl2F) and unsaturated compounds (e.g., CH2xe2x95x90CF2, CH2xe2x95x90CClF and CH2xe2x95x90CCl2).
Included in this invention is the reaction of an acyclic saturated compound of the formula CnFaXbHc wherein n is at least 2, c is at least 2 and the mole ratio of HCl to the compound is at least about 5:1 to produce a hydrogen-containing olefinic product. Also included is the reaction of an acyclic saturated compound of the formula CnFaXbHc wherein n is 2, c is 1 and the mole ratio of HCl to the compound is at least about 5:1 to produce a perhalogenated olefinic product. For example, CF3CF2H may be reacted with HCl (preferably in a molar ratio of HCl:CF3CF2H of at least about 6:1) in the presence of a catalyst (e.g., an aluminum fluoride catalyst) to produce CCl2xe2x95x90CCl2 as the major halogenated hydrocarbon reaction product. Also included is the reaction of an acyclic saturated compound of the formula CnFaXbHc where n is at least 2 (e.g., n is 2 or n is 3) and the mole ratio of HCl to the compound is about 5:1 or less (e.g., from 2:1 to 5:1) at an elevated temperature less than about 350xc2x0 C. (e.g., 250xc2x0 C. to 325xc2x0 C.) to produce compounds of reduced fluorine content which are primarily (i.e., more than 50 mole percent) saturated compounds. Other embodiments involve the reaction of an acyclic saturated compound of the formula CFaXbHc wherein b is 0 to 2.
The invention includes reactions of HCl with mixtures of compounds of the formula CnFaXbHc with each other and/or with other organic compounds such as ethers (e.g., dimethylether), alcohols (e.g., methanol) and hydrocarbons (e.g., propane and/or cyclohexane). In some embodiments, the mixtures are azeotropic. Examples of acyclic saturated compounds which may be reacted with HCl in accordance with this invention include CH2FCF3, CHF3, CHF2CF3, CH3CF3, CH3CHF2, CHCl2F, CHClF2, CHCl2CF3, CHClFCF3, CH2ClCF3, CH3CF2Cl, CHBrF2 and CF3CHBrF.
Chlorine may be present in some process embodiments, either as an initial reactant or as an in-situ formed product. Of note are reactions wherein Cl2 is present during the reaction and a perhalogenated product is produced.
Suitable catalysts which can be used for reducing the fluorine content of the starting materials by reaction with HCl include vapor phase fluorination catalysts. Catalysts which may be used in accordance with this invention include metals (including elemental metals, metal oxides and/or other metal salts); alumina; fluorided alumina; aluminum fluoride; metals on alumina; metals on aluminum fluoride; magnesium fluoride on aluminum fluoride; metals on fluorided alumina; alumina on carbon; aluminum fluoride on carbon; fluorided alumina on carbon; metals on carbon; chromium catalysts (e.g., Cr2O3 by itself or with other metals such as Mg and/or Zn); mixtures of metals, aluminum fluoride, and graphite; and chromium-magnesium optionally on graphite. Suitable metals for use as catalysts (optionally on alumina, aluminum fluoride, fluorided alumina or carbon) include chromium, Group VIII metals (iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum), Group VIIB metals (manganese, rhenium), Group IIIB metals (scandium, yttrium, lanthanum), Group IB metals (copper, silver, gold), zinc and/or metals having an atomic number of 58 through 71 (cerium, praseodymium, neodymium, promethium, samarium, europium, gadolonium, terbium, dysprosium, holmiun, eribum, thulium, ytterbium or lutetium). Preferably, when used with a support, the total metal content of the catalyst will be from about 0.1 to 20 percent by weight; typically, from about 0.1 to 10 percent by weight.
Fluorided alumina and aluminum fluoride can be prepared as described in U.S. Pat. No. 4,902,838. Metals on aluminum fluoride and metals on fluorided alumina can be prepared by procedures described in U.S. Pat. No. 4,766,260. Catalysts comprising chromium are well known in the art (see e.g., U.S. Pat. No. 5,036,036). Chromium supported on alumina can be prepared as described in U.S. Pat. No. 3,541,165. Chromium supported on carbon can be prepared as described in U.S. Pat. No. 3,632,834. Catalysts comprising chromium and magnesium may be prepared as described in Canadian Patent No. 2,025,145. Other metals and magnesium optionally on graphite can be prepared in a similar manner to the latter patent. Preferred catalysts include catalysts comprising aluminum fluoride and catalysts comprising chromium oxide.
Weak catalysts for this reaction such as silicon carbide may also be used.
The reaction of the acyclic saturated compound of the formula CnFaXbHc with HCl in the presence of the catalysts of the instant invention is suitably conducted at a temperature within the range of from about 250xc2x0 C. to 450xc2x0 C., preferably from about 300xc2x0 C. to 400xc2x0 C., and most preferably from about 325xc2x0 C. to about 375xc2x0 C. The contact time is typically from about 1 to about 120 seconds, preferably from about 5 to about 60 seconds.
The amount of HCl should be at least a stoichiometric amount. Generally, the molar ratio of HCl to the acyclic saturated compound can range from about 1:1 to about 100:1, preferably about 3:1 to 50:1, and more preferably about 5:1 to 20:1.
In general, with a given catalyst composition, the higher the temperature and the longer the contact time, the greater is the conversion of fluorinated products and the greater is the production of polychlorinated products. The above variables can be balanced, one against the other, so that the formation of lower fluorine substituted products is maximized.
The reaction products may normally be separated by conventional techniques, such as distillation. Some of the reaction products will have desired properties for commercial use by themselves, or as intermediates for making other commercial products. Others, such as CHClxe2x95x90CCl2, CCl2xe2x95x90CCl2, CHCl3, etc. can be recycled back to reactors which are being used for the synthesis of hydrofluorocarbons and hydrohalofluorocarbons. For example, vapor-phase processes for manufacturing CF3CHCl2 and/or CF3CHFCl by hydrofluorination of CCl2xe2x95x90CCl2 often produce substantial amounts of CF3CF2H by-product; and the process of this invention may be used to obtain CCl2xe2x95x90CCl2 (and HF) for use as starting materials for the hydrofluorination. The process of this invention provides a method of utilizing substantially all of a halogenated hydrocarbon plant""s products. This utility has the benefit of providing a manufacturing facility with minimum waste, and therefore, minimum environmental impact.
The reaction of the acyclic saturated compound with HCl may be conducted in any suitable reactor, including fixed and fluidized bed reactors. The reaction vessel should be constructed from materials which are resistant to the corrosive effects of hydrogen fluoride such as Inconel(trademark) nickel alloy and Hastelloy(trademark) nickel alloy.
Pressure is not critical. Atmospheric and superatmospheric pressures are the most convenient and are therefore preferred.
Practice of the invention will become further apparent from the following non-limiting examples.